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Who is running 37"-40" tires on the diesel

Phil3333

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Any need for a regear?
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Odubi

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Any need for a regear?
I run 37s. I donā€™t believe regearing Is necessary but I do find that she does ride in 8th as much as before. Granted Iā€™ve also added a decked system, heavy full height rack and a clam shell tent so Iā€™ve also increased a fair amount of weight.
 

iadslgladiator

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Daily driving on 37's with stock gears is perfect. If you plan on pulling a largish enclosed trailer/camper frequently I think you'd be happier with 4:10's. By no means do I think its "mandatory" just think having a little more gear is beneficial.

I've never had anything larger than 37's so can't offer an opinion on that.
 

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Several threads here on this subject, I'm running 37's and see no reason to regear including towing.
 

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QuickOne

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Same here - 37s and no need to regear. The diesel likes the low-rpm hustle of the 37s. They live in its power band.
 

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Just because it can turn them doesn't mean it's doing so efficiently, any insights into MPG losses? Ideally diesels like to cruise just ahead of the torque peak so any speed loss from hills etc gets absorbed into making more power so as tire diameter increases gearing should likewise to keep your cruise rpm at a given speed constant.
 
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Phil3333

Phil3333

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I have been running 38s I figured on regearing I don't think it is necessary still runs in 8th gear at freeway speed plenty of power
 

CerOf

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Keep in mind, 8th gear is .67. 7th gear is .84.

The transmission dropping from 8th to 7th on an incline isn't a big deal. I doubt with 37s youā€™ll drop more than 1 gear in all but the steeper to steepest grades.
 

ACAD_Cowboy

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ZF 8HP75 5.0000 / 3.2000 / 2.1429 / 1.720 / 1.3139 / 1.0000 / 0.8221 / 0.6400 / 3.4560 (Reverse)
 
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Odubi

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Iā€™ve had 37s on mine for 20k and what I have noticed. I drive a 600km round trip every two weeks all highway with some minor inclines. Stock I did this entire drive in 8th gear unless Iā€™m passing at 23mpg average. Now I spend 30% of the drive in 7th with 19mpg. So is in necessary No, would going a step up to bring it back to stock increase the drive ability, Iā€™d assume yes.
 

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Okay time for some fun, to me I guess.

The L630 Gen III is listed as 480 lb-ft @ 1600rpm, 260hp @ 3600rpm with fueling cut off at 4800rpm. The 8HP75 has a revised program for shorter shifts when paired with the L630G3.

Using the stock 285/70/17 tires and the factory 3.73 gearing versus a BFG KM3 37x13.5x17 and 3.73

At torque peak in 8th gear we go from 65.2mph to 72.8mph anf 55 happening at 1350rpm and 1210rpm respectively. Tire weights are 67lb and 82lb respectively. The nominal diameters are 32.8 and 36.5.

Running the numbers to return the 37x13.5x17 KM3 to the RPM standard of the stock tire you'd need to regear to 4.56 which would put 55 at 1478, peak torque at 59.5.

A few hundred rpm doesn't sound like much but when coupled to 60lb increase in tire weight, those few hundred rpm aren't as easy to make back in terms of boost and cooling.

See attached data.
 

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WAJTRD

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Running 37's, hardshell roof top tent and rack so always ~400lbs of stuff in the back. No need to regear in my opinion.

Living in the mountains of WA, I average 21.5mpg on the diesel.
 

@californiajeeping

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Okay time for some fun, to me I guess.

The L630 Gen III is listed as 480 lb-ft @ 1600rpm, 260hp @ 3600rpm with fueling cut off at 4800rpm. The 8HP75 has a revised program for shorter shifts when paired with the L630G3.

Using the stock 285/70/17 tires and the factory 3.73 gearing versus a BFG KM3 37x13.5x17 and 3.73

At torque peak in 8th gear we go from 65.2mph to 72.8mph anf 55 happening at 1350rpm and 1210rpm respectively. Tire weights are 67lb and 82lb respectively. The nominal diameters are 32.8 and 36.5.

Running the numbers to return the 37x13.5x17 KM3 to the RPM standard of the stock tire you'd need to regear to 4.56 which would put 55 at 1478, peak torque at 59.5.

A few hundred rpm doesn't sound like much but when coupled to 60lb increase in tire weight, those few hundred rpm aren't as easy to make back in terms of boost and cooling.

See attached data.
Good post. Iā€™m running 38s and the diesel donā€™t care. It just make boost and chooch
 

SLC Rubicon

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I've got 37s and get between 20 and 22 on all tanks. I live in Utah and like to drive fast and haven't once considered re gearing.
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